The ocean is the biggest carbon sink, that means it stores carbon dioxide. An estimated 33% of the carbon dioxide from human activity released into the atmosphere dissolves into oceans, rivers and lakes, thus lessen the GHG effects. But in the ocean carbon dioxide forms carbonic acid, decreasing the pH-value. This process takes place much faster than at any time in the past 300 million years, preventing cycling processes to compensate and animals to adapt. Slowed or even reversed calcification poses the risk of fundamentally altering marine food webs, diminishing some organism like calcifying zooplankton, Haptophyte (a phytoplankton species that needs calcium carbonate), stony corals or coralline algae (a red algae species strengthening the reef structure) and increasing others like other phytoplankton species or toxic algae. The changing chemistry of oceans affects lots of animal behaviors, like hearing, echolocation or communication (due to altered acoustic properties of seawater) or smelling, as well as the acid-base balance inside every single cell.